United States
Environmental Protection
Agency
Robert S. Kerr Environmental
Research Laboratory
Ada OK 74820
Research and Development
EPA-600/S2-84-044 March 1984
SER& Project Summary
On-Farm Improvements to Reduce
Sediment and Nutrients in Irrigation
Return Flow
L.G. King, B.L. McNeal, F.A. Ziari, and S.C. Matulich
Research on an 800-hectare irrigated
tract consisting of a hydrologic sub-
basin with well-defined surface drainage
covered five complete irrigation seasons
(1977-81). This predominantly furrow-
irrigated area was located within central
Washington's Columbia Basin Project.
The cooperative research project
studied the effects of on-farm im-
provements to reduce the discharge of
sediment and nutrients (nitrogen and
phosphorus) from the tract via irrigation
return flow. Both technical and financial
(cost-sharing of construction) help were
given to the participating farmers. Be-
tween the 1978 and 1979 irrigation
seasons, facilities on various farms were
constructed with the grant providing 70
percent (up to a pre-determined maxi-
mum amount) and the farmer providing
30 percent (plus any excess above the
pre-determined maximum) of the costs.
A goal of about $125 per hectare bene-
fited was set as a maximum cost share
to be provided by research grant funds.
The constructed facilities included pipes
to convey center pivot overflow and fur-
row tailwater to improved drains, sedi-
ment basins, sediment mini-basins,
concrete lining of head ditches, gated
pipe systems, and conversion of furrow-
irrigated land to sprinkler (both center
pivot and solid set). Approximately
$70,000 of grant funds were spent on
cost-sharing of construction.
Results showed that construction of
proper sediment control facilities on
furrow-irrigated farms greatly reduced
the discharge of sediment from the
overall tract. The 3-year average sedi-
ment discharge from the area after con-
struction of on-farm improvements was
about twenty percent of the 2-year
average discharge before construction.
The irrigation return flows decreased
about three percent following con-
struction.
While reductions in phosphorus loss
were significant, results snowed that
measures which controlled sediment
loss were not equally effective in con-
trolling phosphorus loss. The 3-year
average phosphorus discharge after
construction was 51 percent of the
2-year average before construction. The
difference in effectiveness of control
measures for sediment and phosphorus
was attributed to the association of
phosphorus with clay-sized sediment
particles which are not easily settled
once they become suspended in irriga-
tion tailwater. End-of-field sedi-
ment/phosphorus ratios were often
about 1,500 whereas these ratios for
water in the main drain leaving the en-
tire study area were only about half this
value.
The project activities had little effect
upon the discharge of nitrogen from this
irrigated tract during the period of
study. A considerable part of the area
was served by subsurface drainage
systems, which discharged into the
main surface drain through the area. The
water from the surface and subsurface
sources was comingled in the main
drain as it left the irrigated tract.
Discharge of nitrogen was about 20 to
30 kg per hectare per year during the
study period.
Techniques were devised to reason-
ably separate the effects of ashfall
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deposited into the study area by the May
18, 1980 eruption of Mount St. Helens
from the effects of research project ac-
tivities related to sediment and phos-
phorus discharges. The effects of the
ashfall were mainly confined to a two-
week period immediately following the
eruption.
Results presented in this report ad-
dress the problems of sediment and
nutrient discharges on three basic
levels: individual furrows, individual
fields, and the total 800-hectare study
area. Models are presented which deal
with sediment loss, nitrogen loss and
economic motivation for BMP adoption.
This Project Summary was developed
by EPA's Robert S. Kerr Environmental
Research Laboratory, Ada, OK, to an-
nounce key findings of the research pro-
ject that is fully documented in a
separate report of the same title (see
Project Report ordering information at
back).
Introduction
Irrigation return flow (i.e., water which
returns to streams and rivers after being
diverted and applied to the land as irrigation)
can carry many substances classified as
pollutants. In the Pacific Northwest, some
of the major pollutants in irrigation return
flow have been identified as sediment,
nitrates, nematodes, phosphorus (attached
to sediment), bacteria, and increased
temperature. In regulations promulgated pur-
suant to PL 92-500 much of the irrigation
return flow was classified as point sources.
For a point source discharge, a "National
Pollutant Discharge Elimination System"
(NPDES) permit was required by PL 92-500.
The State of Washington Department of
Ecology (DOE) was authorized by the U.S.
Environmental Protection Agency (EPA) to
issue NPDES permits for discharges into the
waters within the jurisdiction of the State.
By late 1974, the DOE was well underway
with the development of a permit program.
During the development of this program, it
became apparent that the greatest reduction
of total sediment in irrigation return flow
would be realized by change of practices on
the individual farms. Once the return water
reaches a common drain, opportunities for
sediment removal are considerably
restricted.
Because of court action, the DOE (in State
of Washington) did not issue any of the ir-
rigation return flow permits which were
being prepared. Instead, a cooperative pro-
gram to improve farming practices in order
to reduce the sediment delivered to the
Yakima River via irrigation return flow was
begun. This program identified the Sulphur
Creek drainage near Sunnyside, Wash-
ington, as a problem area which should
receive high priority. In 1975, the Sulphur
Creek Demonstration Project was started. By
the end of the 1976 irrigation season, it was
evident that this site had many character-
istics making it unsuitable for obtaining the
desired information to fully evaluate the
benefits of on-farm changes in reducing sedi-
ment discharge to the Yakima River via ir-
rigation return flow. A smaller, more
compact, drainage with well-defined
hydrologic boundaries having fewer sources
of inflow and points of discharge was need-
ed. Farmer participation had not been as
great in the Sulphur Creek project as had
been anticipated and those farmers who
were participating were widely scattered
throughout the drainage. Incentives for par-
ticipation apparently had not been large
enough.
Selection of a site for the work reported
herein began in late 1976. It was decided that
the greatest benefit to the State could be
achieved by locating the study area within
the Columbia Basin rather than the Yakima
Valley. A site within the Columbia Basin
would allow the project to be separated from
the Sulphur Creek activities. By such separa-
tion the public would not likely be confused
by the different approaches of the two
studies. Criteria for selection of this site were
the following:
A. Primarily surface irrigated
B. Existing sediment problems in irrigation
return flow
C. Single discharge point for return flow
D. Approximately 800 hectare
E. Well defined drainage system for sur-
face flows
F. Several farmers
G. Range of crops
H. Range of slops
I. Soils typical of much of the Columbia
Basin
J. Indications of farmers' willingness to
participate in the study.
In the fall of 1976, the principal investigator
met with personnel of the three Columbia
Basin irrigation districts, (Quincy Columbia
Basin Irrigation District [QCBID], East Col-
umbia Basin Irrigation District [ECBID], and
South Columbia Basin Irrigation District
[SCBID1; with the help of the directors and
district personnel two alternate sites were
selected. Careful review of the sites indicated
that one site was clearly superior to the other
in light of the foregoing criteria. In early 1977,
the study site was selected in Block 86 on
the Royal Slope west of Othello, Wash-
ington. The site lies within the QCBID and
Grant County. The Geological Survey
(USGS), the Bureau of Reclamation
(USBR), and the three Columbia Basin irriga-
tion districts agreed to monitor the irrigation
supply and drainage of the study area dur-
ing the 1977 irrigation season to obtain
background data prior to the start of the
research project. This monitoring continued
throughout the duration of the project under
joint funding by DOE, USGS and USBR.
In the project, both technical and finan-
cial help was given to the individual farmers
for on-farm improvements to reduce sedi-
ment and nutrients leaving their farms in ir-
rigation return flow. The first year of the
project (the 1978 irrigation season) was spent
analyzing the operation of all the farms in the
study area, gathering data needed before
changes were made. Design proceeded as
soon as possible to allow for construction of
necessary structures prior to the start of the
1979 irrigation season.
Since farmers were to be provided finan-
cial help in construction of facilities, par-
ticipation was expected to be high. The goal
was to have all farmers in the study area par-
ticipating in the project. The response of the
farmers to the project at an information
meeting held March 8, 1977 indicated that
this goal was attainable. The on-farm
facilities were constructed under a cost-
sharing arrangement. The research grant
provided 70 percent of the cost of capital im-
provements up to a maximum amount. The
farmer provided the other 30 percent and all
costs exceeding the amount agreed upon
prior to the start of construction. A goal of
about $125 per hectare benefited was set as
a maximum cost share to be provided by the
research grant funds.
In 1977, the U.S. Congress passed PL
95-217 which expressly placed irrigation
return flow under Section 208 and removed
it from Section 402, NPDES permits, of PL
92-500. The planning activities under Sec-
tion 208 in Washington resulted in a program
of voluntary farmer participation to reduce
sediment carried by irrigation return flows.
Objectives
The overall goal of this project was to
assist in developing and implementing a pro-
gram for reducing the negative impacts of
irrigation return flows on water quality. It
was recognized that reduction of pollution
from these sources is most effectively
achieved by improvement of farming prac-
tices on individual farms. It was anticipated
that the farming practices to be studied
under this project would include the best
management practices (BMPs) then being
developed by the local water quality com-
mittee involved in the 208 planning process
for irrigated agriculture. Implementation of
the 208 plans for irrigated agriculture was a
significant component of this research
project.
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k second general goal of this project was
ielect a study area in which a high degree
participation by the farmer and significant
inges of farming practices could be
lieved.
Jecause of the importance of this work
the local area and to the state, another
al was the timely dissemination of infar-
ction via county extension agents, periodic
teetings with the three Columbia Basin ir-
gation districts and conservation districts,
nd annual field days at the study site.
Results and Conclusions
A cost-sharing program was established
or the Block 86 study area to provide a
neans of constructing facilities on the par-
icipating farmer's land. Full ownership of
lese facilities rests with the land owner. The
;ost share contributed by the research grant
vas viewed as an incentive for the farmer's
larticipation and an aid to provide facilities
lecessary for the research work. All facilities
vere designed by the faculty members of
Vashington State University who were
issociated with the research project. The on-
arm facilities included buried pipelines,
Concrete-lined head ditches, gated pipe
YStems, sprinkler systems (both center-
wot and solid-set), and sediment basins. A
otal of $69,825 of research grant funds were
ipent on cost-sharing for construction of on-
arm facilities. Since certain areas received
>enefit from more than one of the facilities,
i cost per hectare directly benefited is dif-
icult to obtain. Data were collected from
hroughout the study area each year in order
o evaluate the magnitude of pollution from
rrigation return flows. These included sam-
)l ng of: (1) losses from the study area at the
n lin drains, (2) losses from individual fields,
it d (3) losses from individual furrows.
The results of this research project show
.hat effective reduction of sediment dis-
;harge from individual fields and from the
otal study area was accomplished by con-
struction of on-farm facilities. The 3-year
iverage sediment discharge from the area
ifter construction of on-farm improvements
was about 20 percent of the 2-year average
discharge before construction. The irrigation
eturn flows decreased only about three per-
snt following construction.
Funds provided for construction of on-
rm facilities averaged less than 90 dollars
i sr hectare benefited. It is extremely difficult
i) assess the value of total project activities
nd visibility of professional people in ac-
iomplishing the observed reduction of sedi-
lent discharge. Expenditures of similar
apital construction assistance in different
reas in absence of these other activities may
ir may not produce the same effects.
Sediment basins were the most successful
of measures used in this study for reducing
sediment discharge from irrigated fields.
Sediment basins constructed by farmers
without technical assistance usually do not
have sufficient capacity to trap sediment for
a complete irrigation season. In 1981, the
sediment basins removed from 53 to 85 per-
cent of all incoming sediments with an
average of 66 percent. When a single under-
sized basin was used to attempt to retain
sediment in tailwater from several farm units,
the basin filled completely after only two ir-
rigations.
Certain problem situations, such as steep
tailwater collection ditches and lack of a con-
veyance channel adequate for sprinkler pond
overflows, were successfully corrected in the
study area. Check dams were used in the
steep ditches and the overflow from center
pivots was piped to an improved open drain.
Reduction of sediment discharge should
not be equilibrated with reduction of erosion.
Properly designed and maintained sediment
basins will reduce sediment discharge while
on-field erosion may continue unchecked.
On one particular field in the study area, the
soil surface elevation at the head of the field
had dropped nearly one meter since irriga-
tion began in the 1950's.
Reduction of sediment discharge does not
necessarily accomplish reduction of
phosphorus discharge. Once the soil par-
ticles have been suspended in the water, nor-
mal settling will be more effective in
removing sediment than phosphorus
because of the association of phosphorus
with clay-sized sediment particles which are
not easily settled once they become
suspended in irrigation tailwater. The 3-year
average phosphorus discharge from the total
study area after construction of on-farm im-
provements was 51 percent of the 2-year
average before construction. End-of-field
sediment/phosphorus ratios were often
about 1,500 whereas these ratios for water
in the main drain leaving the entire study area
were only about half this value.
Nitrogen discharge from an irrigated area
is not subject to effective control by prac-
tices used for this research project. Model-
ing results indicated that considerable time
may be required to observe any change in
nitrogen discharge as a result of a practice
change. Measured nitrogen discharge from
the total study area was not affected by pro-
ject activities during the period of study. A
considerable part of the area was served by
subsurface drainage systems which dis-
charged into the main surface drain through
the area. The water from surface and sub-
surface sources was comingled in the main
drain as it left the irrigated tract. Discharge
of nitrogen was about 20 to 30 kg per hec-
tare per year during the study period.
The ashfall deposited onto the study area
by the May 18, 1980 eruption of Mount St.
Helens did not invalidate the research find-
ings. Techniques were developed and dem-
onstrated to be successful for separating the
effects of the ashfall in contrast to the ef-
fects of the research project activities upon
the discharge of sediment and phosphorus
from the area. The effects of the ashfall were
mainly confined to a 2-week period imme-
diately following the eruption.
The crop grown on a particular field has
a significant effect on the sediment loss.
Row crops such as sugar beets, beans, and
corn produce much more sediment than
close-growing crops such as wheat.
Scheduling of irrigation has an effect on
the seasonal sediment loss from a field.
Studies showed that reducing the number
of irrigations on beans could reduce the total
sediment loss for the season without lower-
ing the yield.
Use of methods to control the stream size
in individual furrows can reduce sediment in
tailwater. There is a definite need for
automated or semi-automated furrow irriga-
tion systems. Cutback irrigation practices are
effective in reducing sediment, but are not
very popular with farmers because of large
labor requirements with irrigation systems
presently on the farms.
The Imhoff cone, using a 15-minute settl-
ing time, was tested as a device for measur-
ing suspended sediment in irrigation
tailwater. For sandy loam and loamy sand
soil textures, the Imhoff cone reading cor-
related well with suspended sediment con-
centration measured with standard methods.
These two textures account for approximate-
ly 31 percent of the land in Washington
which is furrow irrigated. Another 62 percent
of furrow-irrigated land is silt loam and loam.
Use of the Imhoff cone may be acceptable
for these textures. Perhaps the best use of
the Imhoff cone for irrigated agriculture
would be as a tool for comparing the relative
effectiveness of various practices in reduc-
ing sediment loss from a given field. Such
use should be beneficial as an evaluation aid
to a farmer, and to personnel of conserva-
tion or irrigation districts. The Imhoff cone
should not be used as a regulatory standard.
Working models were developed to
describe the nitrogen movement and loss
from furrow-irrigated land and to describe
the discharge of sediment from individual ir-
rigation furrows. The models are researchers'
tools and are not yet ready for more
widespread use.
Economic modeling demonstrated the im-
portance of tax considerations in motivating
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BMP adoption. Immediate attention should
be given to existing institutions and pro-
grams that provide some incentive to adopt
pollution abatement technologies. A pro-
gram of variable incentives depending upon
farm size and debt/equity position would be
the most efficient expenditure of funds to
produce the adoption of BMPs.
Recommendations
Incentive programs must recognize the
need to reduce the on-field erosion as well
as sediment discharge for furrow-irrigated
land. Sediment basins should be used in con-
junction with improved water management.
A full program of the farmer's assistance is
necessary to obtain use of proper water
management primarily including appropriate
furrow stream size, irrigation set time, and
length of run. Development of systems for
automation or semi-automation of furrow-
irrigation will greatly assist efforts to obtain
adoption of the changes in on-farm water
management needed for effective control of
on-field erosion and of sediment and phos-
phorus discharge. Development of these
systems should receive federal and state
support.
Incentive programs must also address the
after-tax determination of cost effectiveness
of control measures. The findings of this
research support a program of variable in-
centives depending upon farm size and
debt/equity position of the land owner.
Work should continue on model develop-
ment of sediment discharge from individual
furrows. This model should be used to study
effects of better water management on field-
wide and area-wide sediment losses. The
model should be further developed to han-
dle erosion and deposition of sediment along
the furrow.
Farmers should be required to pipe center
pivot sprinkler overflows to an acceptable im-
proved drain, especially for new installation
of center pivots. Steep tailwater ditches
should be piped or have check dams in-
stalled. Technical assistance should be pn
vided to farmers for proper sizing and desk
of sediment basins.
L G. King, B. L McNeal. F. A. Ziari, andS. C. Matulich are with Washington State
University, Pullman, WA 99164.
James P. Law. Jr., is the EPA Project Officer (see below).
The complete report, entitled "On-Farm Improvements to Reduce Sediment and
Nutrients in Irrigation Return Flow," (Order No. PB 84-155 217: Cost: $ 19.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Robert S. Kerr Environmental Research Laboratory
U.S. Environmental Protection Agency
P.O. Box 1198
Ada, OK 74820
U.S GOVERNMENT PRINTING OFFICE; 1984 — 759 015/7632
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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